Generally, a gas turbine compressor of the type identified above comprises a plurality of stages including a first fixed stage comprising a plurality of first adjustable vanes and a further fixed stage, which comprises an inner ring extending about a first axis; an outer ring arranged about the inner ring and coaxial with the inner ring; and a plurality of second adjustable vanes, each of which extends about a second axis in essentially radial direction with respect to the first axis between the inner ring and the outer ring.
A gas turbine compressor is crossed by a flow of air in axial direction: the function of the first fixed stage is to convey and orient the flow of air so as to optimise the action of the flow of air on a first impeller arranged directly downstream of the first fixed stage. Similarly, the function of the further fixed stage is to convey and orient the flow of air so as to optimise the action of the flow of air on a further impeller arranged directly downstream of the further fixed stage.
The orientation of the flow of air is obtained by adjusting the orientation of the first vanes in the first fixed stage and the orientation of the second vanes in the further fixed stage.
For this purpose, a gas turbine compressor of the known type is equipped with an adjusting device which allows to simultaneously adjust the orientation of the first vanes and of the second vanes.
This adjusting device has been proven inadequate because it requires the identification of a half-measure adjustment position: in other words, an optimal orientation of the first vanes does not correspond to an optimal orientation of the second vanes. For this reason, the functions of the compressor, and consequently of the gas turbine, cannot be optimised.
Furthermore, the adjusting device of the known type requires to adapt the shape and dimensions of the further fixed stage to the structure of the adjustment device.